A shock absorber is provided between a vehicle body and tires in an automobile and absorbs vibration of the vehicle body caused by a bumpy road surface, wobble generated at sudden acceleration and sudden braking, and the like. The shock absorber is typically attached diagonally since such a diagonally attached shock absorber is superior to a vertically attached shock absorber in riding comfort of the automobile. With this arrangement, a lateral force, which is caused by a bending moment generated by expansion and contraction of the shock absorber, is applied to the shock absorber. In order to smoothly expand and contract the shock absorber while the lateral force is applied, it is required to decrease friction in a bearing (guide bush) and improve wear resistance of a shock absorber fluid (SAF).
In response to such a demand, for instance, there is provided a hydraulic fluid composition for a shock absorber including: (a) a base oil; (b) at least one compound selected from the group consisting of a phosphate ester, a phosphite ester and a phosphate ester amine salt; and (c) alkanol amine (see Patent Literature 1). Moreover, there is provided a fluid composition for an active suspension including: (A) a phosphite ester; (B) an aliphatic amine oiliness agent; and (C) fatty acid, naphthenic acid, an ester thereof, or a mixture thereof, as essential components each at a predetermined content in a lubricating base oil (see Patent Literature 2).